General and special purpose host computers often include provisions for various peripheral functionality, such as a communications modem, memory expansion, or an add on hard disk drive. In order to facilitate the addition of various peripherals the Personal Computer Memory Card International Association (PCMCIA) has endeavored to standardize a family of peripheral cards with a requisite PCMCIA interface. The PCMCIA defined parameters can be found in the PC Card Standard Release 2.0 document, published by the Personal Computer Memory Card International Association, 1030B East Duane Avenue, Sunnyvale Calif. and incorporated herein by reference. The defined parameters include physical parameters such as dimensions, input/output connections such as control, address, and data buses, signal parameters such as operating levels and impedances, and certain operating procedures.
Among other specified attributes the physical interface defined by the PCMCIA standard is a 68-pin connection. To facilitate a logical interface between a host computer and a PCMCIA interface port it has been deemed necessary to define a manner or mechanism for determining whether a peripheral function is available at a PCMCIA port. The PCMCIA standard defines two signals at the interface port, referred to as card detect 1 and card detect 2 (CD1 and CD2), that allow the host computer to detect the presence of a card or more generally determine whether a peripheral function is available at the interface port. When CD1 and CD2 are asserted to a logic low the host computer may assume a PCMCIA card is present or plugged into the PCMCIA physical interface socket that is, typically, part of the host computer. Current PCMCIA peripherals or cards implement the card detection function by simply connecting the CD1 and CD2 connector pins to a ground potential on the card's printed circuit board (PCB). Since the peripheral or card is presumed to be powered by the host computer through the VCC (+5 V power) and GND pins on the 68-pin connector or interface, CD1 and CD2 get immediately asserted to the logic low level when the peripheral function is physically interfaced to the PCMCIA port by, for example, plugging the PCMCIA card into the host's PCMCIA card socket.
The PCMCIA standard defines the card detection scheme as follows. Initially, CD1 and CD2 are asserted low and the host detects that a card has been plugged into the socket. The host turns on the VCC supply for the socket and asserts the RESET signal to logic high and then logic low to reset the card. The host then reads the Card Information Structure (CIS) of the card to determine the configuration information or characteristics of the card. After reading the CIS, the host can use the card according to the functionality that is defined in the CIS. For example, if information in the CIS indicates that the card is a modem card, the host will use the card as a modem. If the CIS indicates that the card is a memory card, the host can use the card as its extended memory or as a place for file storage. Allowed variations of the contents of the CIS are defined by the PCMCIA standard.
For many peripheral functions such as a wireline modem, a memory card, or other relatively passive functions having no relevant purposes other than in conjunction with a host computer the present approach appears to be satisfactory and clearly within the limits envisioned by the FCMCIA standards. However where the peripheral function has meaningful independent or partially independent functionality the above standardized procedures may not be acceptable or at least not optimal. In these cases the peripheral function, often embodied on a PCMCIA compatible card likely will have, for example, an independent or at least supplemental power supply that may include an on/off switch. Among others, one problem this may present is the possibility that the peripheral function is physically interfaced or present at the PCMCIA port and its power supply is disabled by, for example, the on/off switch being in an `off` state. Under these circumstances the card should not assert the CD1 and CD2 lines to a logic low because when it is not powered up the host cannot communicate with it. This problem is further compounded if the peripheral function is actually more than one function and only part of the functionality is independent.
One solution to this problem may be to define an alternative non-standardized proprietary interface port. This may be acceptable in the case of a special purpose host when the manufacturer has control of the host computer hardware and operating system software as well as the peripheral function. However this is not typically the case and does requires extra effort to develop the proprietary interface and assure ongoing compatibility with the operating software of the host and the peripheral function could not be made available to the market place at large.
Clearly a need exists for a peripheral function or card that has an adaptive PCMCIA compliant interface that may be generally employed when the peripheral function has independent functionality.